The present invention relates to a switched power supply converter which employs as transformer a piezoelectric transformer to perform a process of converting a voltage supplied from a power source into a different output voltage, suitable for being applied to a load.
The galvanic isolation of the switched power supply converter is provided by the piezoelectric transformer, the operation of which is controlled by the switching of at least one switching element.
The switched power supply converter is of special application, but not exclusively, in telecommunications systems since it offers a high performance with reduced size and weight.
The piezoelectric transformer carries out the transformation of a is voltage applied across some primary terminals to a different voltage produced across some secondary terminals through the mechanical vibration of the piezoelectric transformer, using the piezoelectric effect.
A switched power supply converter with galvanic isolation is adapted for performing a conversion of an input voltage into an output voltage by means of the action of a transformer with windings, i.e., it is a magnetic element.
It is possible to incorporate the power supply converter into a conversion topology with galvanic isolation, which is provided by means of the electromagnetic transformer. Examples of this conversion topology are a forward converter with active clamp and a flyback converter. Both converters have the property of facilitating galvanic isolation, located in different position.
The transformer provides galvanic isolation between the input and the output of the power supply converter, and permits design of the power supply converter with various outputs, as well as compliance with the safety regulations.
However, for the power transformer to provide said properties it must fulfil some design requirements that determine its physical size and weight. Consequently, the power transformer within the switched power supply converter is one of the heaviest and bulkiest devices. Therefore it is necessary to reduce the volume of the power transformer in order to carry out an overall process of miniaturising the switched power supply converter, as well as achieving a reduction in the weight thereof.
The function of transforming the input voltage into a different output voltage may be implemented by a mechanical vibration of a piezoelectric transformer, the volume of which is noticeably less in size than that of the magnetic transformer for an equivalent power level.
Nonetheless, the use of the piezoelectric transformer is not generalised since it has the drawback that in order to work with a high efficiency, the switching elements that govern its operation must work at very high frequency, so that the switching losses increase significantly.
There exists a need to develop a switched power supply converter with galvanic isolation by means of a piezoelectric transformer. The power supply converter has switching elements for implementing the control of the piezoelectric transformer in a simple fashion, which assures the production of a constant and regulated output voltage with a high overall efficiency, a compact size and a reduced weight.
To overcome the problems mentioned above a switched power supply converter is proposed which is reduced in size and weight, while having a high overall efficiency, making it suitable for being mounted together with telecommunications equipment.
It is therefore an object of the present invention to provide a power supply converter that includes a piezoelectric transformer so that its excitation is directed by a driver block the switching elements of which may be switched at a reduced frequency such that the switching losses are minimal.
The switched power supply converter converts a first voltage, supplied from a voltage source, into a second different stabilised voltage by means of a connection in cascade of a DC/AC converter block, followed by a second rectifier connected to a second filter.
The DC/AC converter block comprises a driver block followed by said piezoelectric transformer, connected in cascade. The driver block excites the piezoelectric transformer by means of a pulse train with a first frequency that is less than a resonant frequency of the piezoelectric transformer.
The first frequency corresponds to the frequency at which is switched at least one switching element that the driver block comprises. Then, the switching frequency is a sub-harmonic (sub-multiple) of the resonant frequency of the piezoelectric transformer.